It is often desirable to provide visual information to a living being. Frequently, one wishes to superimpose such visual information upon the being's view of the real world. In other applications, it is desired to shield the user from a view of the environment, providing an exclusive view of the visual information.
Such displays include a number of components including, in a form known as a folded catadioptric head-mounted display, an image generator, a beam splitting fold mirror which receives the image light from the image generator, often via a series of lenses or other optical elements, and sends a fraction, designated the reflected fraction, of such image light to a reflective combiner that is either non-transmissive or both allows light from the real world to pass through such combiner and reflects the image light such that both the real-world light and the image light are transmitted through the beam splitter to the eye of the user, often via another series of lenses or other optical elements. The beam splitter will transmit a fraction, designated the transmitted fraction, of the image light reflected from the combiner. In embodiments in which the combiner is at least partially transmissive, a fraction of the real-world light is also transmitted by the beam splitter.
Previous devices included a number of additional components. Some devices have included corrective optical elements. Other devices have included a depixelator, e.g., as described in PCT/US94/01390 filed Feb. 7, 1994 for "Depixelated Visual Display" (incorporated herein by reference). Still other devices have included apparatus for intensifying the visual display such as those described in PCT/US94/01391, filed Feb. 7, 1994 for "Intensified Visual Display" (incorporated herein by reference).
In general, there are certain disadvantages to including components other than an image generator, beam splitter and reflective combiner. In most cases, each such additional item will contribute to the increased weight of the display device. When the display device is intended to be mounted on the user's head, such additional weight can contribute to discomfort and detract from the ability to move the head quickly and naturally as is desired for virtual reality applications. Furthermore, such additional devices typically must be correctly and precisely aligned and the difficulty and burden of alignment, both during the original manufacture and during any repair or maintenance that may be needed, is compounded by the number of additional components which are included in the device. Furthermore, both the optical design and the mechanical design become complicated when such additional components are included. Moreover, additional components typically increase the cost of the final device.
Accordingly, it would be useful to provide a visual display apparatus which has a reduced or minimized number of components and yet provides a visual display transmitted to the eye of the user having a desirably high quality and intensity of image.